The present invention relates to a device for improving visibility in a vehicle.
Bad visibility at night is a tiring and dangerous situation which is feared by many drivers. As a consequence of bad visibility, the accident frequency is markedly higher at night than while traveling during the day and in good visibility. At night, in particular, the following difficulties occur:                With low beams in case of oncoming traffic, the range of vision is low and misjudged by many drivers. This results in late detection of unlighted obstacles, pedestrians, bicyclists without light and of animals and consequently results in accidents.        The driver is dazzled by the headlights of oncoming vehicles and their reflexes, in particular, when the roadway is wet; the driver drives into a black hole for a short period of time. This is a danger especially to night-blind and aged drivers because of their low visual performance.        In rain, fog and blowing snow, the visibility conditions can even be markedly worse.        
An improvement of visibility at night is achieved by an opto-electronic system which is set forth in German Patent Application DE 40 07 646 A1. The system takes a video image of a traffic scene and displays it to the driver in a suitable manner. The displayed image contains additional information which cannot, or only with difficulty, be detected by the driver with his/her own eyes, especially in darkness, bad weather and fog.
In addition to the normal headlights, the system includes an infrared headlight which uses, as the light source, laser diodes emitting in the near infrared. The laser diodes are operated in a pulsed manner. A CCD camera for taking the video image is accommodated in the roof area of the vehicle. The CCD camera has an electronic shutter which is synchronized with the laser diodes. An optical bandpass filter is attached in front of the camera lens. The video image is shown to the driver on an LCD display. The lasers emit at a wavelength of 810 nm in the near infrared. Since the infrared light is nearly invisible to the human eye and because the luminous intensity used is not higher than with a conventional vehicle headlight, permanent high beam lighting is possible.
The mentioned publication proposes, moreover, to vary the brightness of the lighting as a function of the transmission angle, for example, to illuminate the foreground of a traffic scene less brightly than the background. In this manner, it is possible to compensate for the luminance of the laser light which decreases with distance and to achieve a more uniform illumination of the scene. In particular, a laser beam is swung back and forth in one spatial direction by a tilting mirror and, in a spatial direction perpendicular thereto, is either uniformly expanded or swung rapidly as well to successively scan the traffic scene to be illuminated, and the intensity of the laser light is varied synchronously with the motion of the tilting mirror. However, high demands are placed on the mechanism required for tilting the mirror, which are difficult to meet in the case of a vehicle.